State the equations for the reactions of magnesium hydroxide, aluminium hydroxide and calcium carbonate with hydrochloric acid.

Magnesium hydroxide:

Aluminium hydroxide:

Calcium carbonate:

(i)     one teaspoon (\({\text{5.00 c}}{{\text{m}}^{\text{3}}}\)) of Maalox^® Extra Strength.

(ii)     one tablet of Maalox^® Extra Strength with Anti-gas.

\({\text{Mg(OH}}{{\text{)}}_{\text{2}}} + {\text{2HCl}} \to {\text{MgC}}{{\text{l}}_{\text{2}}} + {\text{2}}{{\text{H}}_{\text{2}}}{\text{O}}\);

\({\text{Al(OH}}{{\text{)}}_3} + {\text{3HCl}} \to {\text{AlC}}{{\text{l}}_3} + {\text{3}}{{\text{H}}_2}{\text{O}}\);

\({\text{CaC}}{{\text{O}}_3} + {\text{2HCl}} \to {\text{CaC}}{{\text{l}}_2} + {{\text{H}}_2}{\text{O}} + {\text{C}}{{\text{O}}_2}\);

Accept H₂CO₃ for H₂O and CO₂.

(i)     amount of \({\text{Mg(OH}}{{\text{)}}_2} = \left( {\frac{{0.400}}{{(24.31 + 32.00 + 2.02)}} = \frac{{0.400}}{{58.33}} = } \right){\text{ }}6.86 \times {10^{ - 3}}{\text{ (mol)}}\)

and amount of \({\text{Al(OH}}{{\text{)}}_3} = \left( {\frac{{0.306}}{{(26.92 + 48.00 + 3.03)}} = \frac{{0.306}}{{77.95}} = } \right){\text{ }}3.93 \times {10^{ - 3}}{\text{ (mol)}}\);

amount of HCl reacting \( = (2 \times 6.86 \times {10^{ - 3}}) + (3 \times 3.93 \times {10^{ - 3}}) = 2.55 \times {10^{ - 2}}{\text{ (mol)}}\) so volume of \(1.00 \times {10^{ - 2}}{\text{ HCl}} = 2.55{\text{ }}({\text{d}}{{\text{m}}^3})\);

No ECF from (a) if formulas of Mg(OH)₂ or Al(OH)₃ are incorrect.

Allow integer values for atomic masses.

Award [2] for correct final answer.

(ii)     amount of \({\text{CaC}}{{\text{O}}_3} = \left( {\frac{{1.000}}{{(40.08 + 12.01 + 48.00)}} = \frac{{1.000}}{{100.09}} = } \right){\text{ }}9.99 \times {10^{ - 3}}{\text{ (mol)}}\);

amount of HCl reacting \( = (2 \times 9.99 \times {10^{ - 3}}) = 2.00 \times {10^{ - 2}}{\text{ (mol)}}\) so volume of \(1.00 \times {10^{ - 2}}{\text{ HCl}} = 2.00{\text{ }}({\text{d}}{{\text{m}}^3})\);

Allow integer values for atomic masses.

Award [2] for correct final answer.

Penalize incorrect answer based on same units mistake once only in 12 (b) (i) and (ii).

Majority of the candidates were able to provide correct balanced equations for part (a) and score the three marks. Many were able to score one mark for completing the calculations in part (b)(i). The most common errors were using the incorrect value for the volume in step 2 or deducing the incorrect amount of HCl reacting. Most candidates performed well on part (b)(ii). For part (c) candidates lost the mark for stating it prevents flatulence.

Majority of the candidates were able to provide correct balanced equations for part (a) and score the three marks. Many were able to score one mark for completing the calculations in part (b)(i). The most common errors were using the incorrect value for the volume in step 2 or deducing the incorrect amount of HCl reacting. Most candidates performed well on part (b)(ii). For part (c) candidates lost the mark for stating it prevents flatulence.